1. Field of the Invention
The subject invention relates to hollow metal doors and, more particularly, metal doors that are of improved design so as to limit the need for detail finishing of welding deformations while maintaining structural integrity of the doors. This design also provides a door with relatively high attenuation of sound but relatively low weight.
1. Description of the Prior Art
Many types of doors have been designed and manufactured in the prior art. Some of these designs were intended, in whole or in part, to limit the degree of finish work that was required to produce a door with a commercially acceptable appearance. The designs varied depending, in part, on the materials from which the door was constructed.
In the case of hollow metal doors, the doors were often constructed of two opposing panels that were fastened together by means of rivets or welds or the like. Usually, there was also some internal reinforcement that was welded to the inside of the door panels to improve the rigidity and other properties of the door or to meet certain industry standards or certification requirements.
One problem with the riveted or welded designs was that the riveting or welding process would often cause local deformation of the door panels that would degrade the appearance of the finished door. To overcome this, the door manufacturer was required to hand-finish the deformed areas by filling and sanding or by other similar methods for finishing the surface of the door panels. In some instances, as for example with brushed stainless steel, these conventional finishing methods could not be used and more elaborate refinishing measures were required. These finishing processes significantly increased the time and cost for manufacturing the door. Accordingly, there was a need in the prior art for a door construction that would avoid disfigurement of the door panels during construction and thereby limit the need for hand finishing of hollow metal doors.
Also in the prior art, there were numerous door designs that were intended to have especially effective sound attenuation properties. Such door designs were developed for applications such as security areas and sound recording studios. Generally, these designs taught that to improve sound attenuation properties, it was necessary to increase the mass of the door. Examples are shown in U.S. Pat. Nos. 3,273,297 and 3,319,738 which disclose the use of a lead sheath inside the door to increase sound attenuation of the door. Other examples are described in U.S. Pat. No. 3,834,487; 4,146,999; and 4,807,411.
According to such teachings, doors that were said to provide high sound attenuation were relatively heavy. This greater weight was the source of many disadvantages. For example, the heavier doors were more difficult to handle and mount and often required structural reinforcement and other custom adaptations. Also, the heavier doors were more expensive to manufacture and ship, and more difficult to operate. To overcome these difficulties and disadvantages, prior art doors incorporated special closure mechanisms and other accessory devices that further increased the cost and installation difficulty.
More recently, additional methodologies such as described in "Pushing the Limits of Acoustical Barrier Performance", John W. Kopec, Noise-Con 90, Univ. of Texas, Oct. 15-17, 1990, pp. 127-132, have been suggested for augmenting sound transmission loss in architectural applications. However, such articles did not describe any structure by which such methodologies could be implemented. Accordingly, there was also a need in the prior art for a door that afforded high sound attenuation, but avoided the disadvantages of the heavier doors.